since u specifically requested casserole recipes, here's a recipe that fits the bill (which i'd assume you'd want to halve based on contessa's recipe)

egg casserole with sausage, mushrooms, and salsa;serves 8-10

12oz bulk italian sausage
2tsp veg oil, if needed
8oz mushrooms, sliced
1/2cup yellow onion, chopped
12 lg eggs
1cup milk
1/2cup salsa
2tbsp flour
1/2tsp baking powder
4cups grated cheddar or monterey jack cheese, divided
1/2tsp salt
fresh ground pepper
sour cream for topping

preheat oven to 350. in a large skillet over medium heat, cook sausage while breaking it up with a spoon until it starts to brown, about 5min. add oil if needed. add mushrooms and onion and cook until tender, about 10min longer. transfer to a lightly sprayed or oiled 9x13" baking dish.

in a bowl, whisk eggs, milk, salsa, flour, and baking powder. add half of the cheese, salt, and pepper to taste. pour over meat mixture. sprinkle with remaining cheese.

bake uncovered until set, about 40min. let stand for 10min serve with sour cream.